In a 3-quart Dutch oven or heavy-bottomed saucepan over medium heat, melt butter. Add onion and saute until translucent (about 5 minutes). Remove pan from heat. Sprinkle chicken with salt and add to pan with paprika, half of the green pepper, and half of the tomato. Cover pan with a tight-fitting lid and cook over very low heat until chicken is tender (1 to 1 1/2 hours). Turn chicken pieces occasionally so that they cook evenly. If necessary, add a few spoonfuls of water to prevent sticking. During the last 15 minutes of cooking, add mushrooms (if used). When chicken is tender transfer to a heated platter. Place pan over medium heat and cook juices, scraping bottom of pan to loosen any burned-on bits. Add a spoonful or so of water to achieve a gravylike consistency, then stir in sour cream (if used) to form a smooth mixture. Pour over chicken and garnish with the remaining green pepper and tomato.

Per serving: 698 Calories; 39g Fat (51% calories from fat); 73g Protein; 12g Carbohydrate; 260mg Cholesterol; 344mg Sodium